1) Field of the Invention
The invention relates to a method for encapsulating electronic components mounted on a carrier. The invention also relates to a device for encapsulating electronic components mounted on a carrier.
2) Description of the Prior Art
In the encapsulation of electronic components, more particularly the encapsulation of semiconductors mounted on a carrier (such as for instance a lead frame), use is made of the so-called “transfer moulding process”. The carrier with electronic components is herein clamped between two mould parts such that mould cavities are defined around the components for encapsulating. Liquid encapsulating material is then introduced into these mould cavities and, after at least partial curing of which the mould parts are moved apart and the carrier with encapsulated electronic components is removed. The feed of encapsulating material takes place by means of one or more plungers with which pressure can be exerted on a supply of encapsulating material provided for this purpose. The plunger is displaceable in a housing into which the not yet liquid encapsulating material is also carried. The encapsulating material is usually placed in the mould in the form of a pellet or in the form of a package enclosed with foil material. The encapsulating material normally consists of a thermocuring epoxy or resin which incorporates a filler. The plunger exerts a pressure on the encapsulating material which is simultaneously heated, as a result of which heating the encapsulating material becomes liquid. As a response to the pressure applied by the plunger, the liquid encapsulating material flows to the heated mould cavity and fills it with encapsulating material. During this displacement of the encapsulating material this material is heated, whereafter it cures thermally (as a result of cross-linking) in the heated mould cavity. This method functions, but the duration of the processing cycle is long and the quality of the encapsulating process is not always readily controllable.
The Japanese patent 62 039215 describes a method for encapsulating products with resin. A mould for use herein is provided with mould cavities, which mould cavities have a lower temperature during the encapsulation than the feed channels and a plunger opening from which the encapsulating material is supplied. Arranged for this purpose in an encapsulating device are different heating elements which can operate independently of each other at different temperature levels.
The Japanese patent 63 179719 describes a method and device for encapsulating products with resin. A mould for use herein is provided with a hot runner section and a a cavity section, in between which heat insulating components are provided. The mould allows to control the temperature of the hot runner and cavity section individually.
The Japanese patent 61 1114824 describes a method and device for moulding products with a resin. To perform melting and curing of the resin effectively, the mould is provided with a pot section from which the resin is provided, and a cavity section, in between which a heat insulating section is provided. The pot section is provided with a separate heater thereby thermally separating it from the cavity section.
The object of the present invention is to provide a method and a device for an improved controllable encapsulation of electronic components and to improve the quality of such an encapsulation.